The XLR cables give an increase in voltage output. sort of DOUBLE the voltage in most situations. My guess is your system is screwed up in one channel via the XLR. like one side of the one channel in the XLR stuff is partially grounded ????
One Channel Lower Output With XLR Cables
I switched to balanced XLR cables from the RCA unbalanced types. When I did this, I noticed via the amp meters, that the right channel had a lower output then the left in all situations, CD-player and tuner. When I switched back to the RCA cables, both channels went back to the same exact output levels. Is this caused by the cables or the balanced outputs of the pre-amp or amp? Does a one meter length of cable really make that much difference in using balanced or non-balanced cables anyway? Thanks.